扩散的前提条件是（）
A.外源化学物具有脂溶性
B.浓度梯度
C.有载体
D.有能量供应
参考答案：B
One to the accident said that the car was racing at full speed and that the driver appeared to be drunk.
A．companion
B．judge
C．witness
D．student
湖堤、海堤应尽可能（）。
A.避开强风
B.避开强风或暴潮正面袭击
C.避开强风或暴潮侧面袭击
D.避开暴潮
